The present invention relates to an expansion type fuse safety device for an accumulator capable of preventing the accumulator from bursting due to a pressure rise in the accumulator caused by an inflation of the contents in the event of, for example, a fire.
There is a risk that the bladder of an accumulator charged with nitrogen gas may burst when its internal pressure is raised due to a temperature rise caused by, for example, a fire in the equipment having the accumulator.
An expansion-type fuse safety device of the type disclosed in Japanese Patent Publication No. 63-63761 (corresponding to U.S. Pat. No. 4,452,275) has been proposed for the purpose of preventing such a danger of bursting. This expansion-type fuse safety device comprises a valve casing having a central gas charging/discharging through hole, a valve attached to the gas charging/discharging hole, a flanged valve casing provided at its lower end with a flange and freely received in a passage bore formed in a pressure vessel from the inner side toward the outer side of the pressure vessel so as to leave a gap between the wall of the passage bore and the peripheral wall surface of the valve casing, a fuse packing interposed between the inner side surface of the pressure vessel and the flange, a tightening nuts screwed to the valve casing at the outer side of the pressure vessel, and a passage formed in the flange so as to provide a communication between the gap and the interior of the pressure vessel when the flange directly contacts with the inner side surface of the pressure vessel.
In the known expansion-type fuse safety device for an accumulator, the valve casing is inserted into the through hole of the fuse packing such that its end projects outward from the device, and the projecting end is tightened by the nut so that the fuse packing is collapsed to provide a seal in the gap between the inner surface of the pressure vessel and the valve casing. As shown in FIG. 5, however, the fuse packing H has a through hole having an inside diameter d1 which is greater than the outside diameter d0 of the valve casing V. Therefore, the fuse packing H is collapsed between the inner surface I of the pressure vessel and the valve casing V so as to have an inside diameter d0 which is smaller than the initial inside diameter d1 thereby making a close contact with the valve casing H. Therefore, the inner peripheral surface VF of the fuse packing exhibits an outward internal buckling by an amount which is 1/2 the length of the difference between the inner circunferential length of the hole of the fuse packing and the circumferential length of the outer peripheral surface of the valve casing, with the result that cracks T are formed to allow leakage.